Which classification of circuit breakers would you find in substations primarily as protective devices?

Vacuum and air circuit breakers are primarily used in substations as protective devices due to their effective performance in high-voltage applications and their ability to interrupt current flow during abnormal conditions. These types of circuit breakers are designed to quickly isolate faults, which is essential in maintaining system integrity and preventing equipment damage in a substation setting.

Vacuum circuit breakers operate by interrupting the arc within a sealed vacuum chamber, making them highly reliable and capable of handling high voltages. Air circuit breakers, on the other hand, use air as an insulating medium, taking advantage of its cooling properties to extinguish the arc efficiently. Both types provide rapid and reliable disconnection of circuits, thereby ensuring the safety and operational continuity of the electrical grid.

Other options involve circuit breaker types that are less common or suitable for the specific demands of substations. For example, gas and oil circuit breakers are typically used in different applications, while hydraulic and pneumatic circuit breakers do not provide the speed and reliability required at substation voltages. Thermal and magnetic circuit breakers are often utilized in residential and commercial applications rather than in substations, as their design may not withstand the rigorous fault conditions often encountered in high-voltage environments.